Lasers are focused, intense light rays of a particular wavelength or wavelength range that may be used for various functions, including reading data from a medium, such as a compact disc, surgical incisions, and creating semiconductor device features. Lasers, however, can be sensitive to temperature variations among structures within the laser generating system. This is due, at least in part, to temperature sensitivity of light refraction indices in various materials used within the laser generating system.
FIG. 1 illustrates a prior art system for generating a laser. The raw light for the laser is generated and amplified by a semiconductor optical amplifier (SOA) chip. The light generated by the SOA enters a wave guide consisting of a clad material, a wave guide core, and series of grating lenses (grating) in order to direct and refine the laser down to a desired wavelength and phase. After light enters the wave guide, it is passed through the grating, which consists of a series of lenses that can pass the desired wavelength and reflect others.
As a result, the light, excluding the desired wavelength, continually reflects from the grating toward the SOA chip. The effect is a laser produced from the wave guide that is of a desired wavelength and phase. The desired wavelength is passed by the grating, whereas the desired phase is produced by placing the grating at a distance from the SOA chip such that the round trip distance of the reflected light is an integer division of the desired wavelength.
Unfortunately, the wave guide clad material and the wave guide core material can change temperature during the course of generating the laser, which can, in turn, change the refraction indices of the wave guide core and clad materials. The refraction index of a material is an indicator of the material's ability to pass or reflect certain frequencies of light. As the refraction index of the clad or core material changes with temperature, less of a particular wavelength of light may be reflected and therefore propagated through the wave guide, resulting in loss of laser intensity or a change in the laser's wavelength.
As a laser travels through the wave guide core, it can be effected by the overall effective refraction index of a substantially cylindrical area surrounding the wave guide core known as the optical mode. FIG. 2 illustrates a cross-sectional view of the wave guide, in which the cross-section of the optical mode is indicated by the red circle. The material within the boundary of the optical mode can effect the light traveling through the core if the temperature of the material changes, due to the resulting change in the refraction index of the material within the optical mode.
Adverse effects on a laser due to temperature sensitivity of refraction indices of materials has been addressed in prior art laser generating systems by using power-consuming devices, such as a thermal electric cooler (TEC). The TEC may be used to cool the wave guide within the optical mode as the wave guide temperature increases from the laser generating process. Through what can be an elaborate technique of detecting the optical mode temperature and adjusting the TEC accordingly, the temperature of the wave guide in the optical mode can remain stable enough to generate a laser that is of substantially the desired wavelength and phase for a particular application.
The TEC, however, can have adverse effects on system power consumption, system cost, and system reliability. Furthermore, the accuracy of the laser's wavelength and phase, using a TEC, is, at least in part, a function of how quickly the TEC can respond to temperature variations within the optical mode without over-compensating for them. As a result, the overall accuracy of the laser can be compromised.